MANILA -- A strong earthquake rocked Southern Mindanao early Sunday morning, according to the Philippine Institute for Volcanology and Seismology.

Phivolcs said that a magnitude 5.9 quake struck off Palimbang, Sultan Kudarat at 12:11 a.m. on April 20.

The temblor was felt as Intensity V in Kiamba, Sarangani. This is classified by Phivolcs as strong and is generally felt by most people indoors and outdoors.

"Many sleeping people are awakened. Some are frightened, some run outdoors. Strong shaking and rocking felt throughout building. Hanging objects swing violently. Dining utensils clatter and clink; some are broken. Small, light and unstable objects may fall or overturn. Liquids spill from filled open containers. Standing vehicles rock noticeably. Shaking of leaves and twigs of trees are noticeable," Phivolcs said on its website.

The quake was also felt as Intensity IV or moderately strong in Kalamansig, Sultan Kudarat; Tupi and T'Boli, South Cotabato; and Maitum, Sarangani.

A second quake with a magnitude of 5.4 struck at 12:50 a.m.

Damage and aftershocks may be expected, the agency advised.